Effective utilization of sunlight, which does not depend on petroleum or atomic energy and produces infinite energy without generating a harmful substance, is one of the challenges which should be addressed by the whole mankind. For example, a photoelectric conversion element which changes sunlight into electric energy is one of the representative examples.
As an attempt which uses sunlight by employing a photoelectric conversion element, there can be cited at present time inorganic system solar cells, such as single crystal silicon, polycrystalline silicon, amorphous silicon, cadmium telluride and indium selenide copper. However, with respect to the silicon mainly applied for these solar cells, it is required highly pure silicon prepared by the advanced refining processes. And the manufacturing process of the solar cells is complicated has the number of steps of the process is large because of the multilayer structure of p-n junction, and the cost of the solar cells is high. Therefore, in order to spread the photoelectric conversion element by making use of sunlight, a development of an easy and simple manufacturing process for the photoelectric conversion element is waited for.
Although an investigation of a photoelectric conversion element using an inorganic material has been made, there has been made a steady investigation of the photoelectric conversion element using an organic material to realize a simpler element. For example, Tang and others reported in 1986 a p-n junction type organic photoelectric conversion element prepared by jointing a perylene tetracarboxylic acid derivative which is n type organic coloring matter and copper phthalocyanine which is p type organic coloring matter (refer to Non-patent document 1).
In order to improve the shortness of the exciton diffusion length and the thinness of the space charge layer which are considered to be a weak point in the organic photoelectric conversion element, there have been investigated several works to greatly increase the area of the p-n junction part prepared by lamination of an organic thin film and to fully secure the number of organic dye molecules which participate in charge separation. The results are coming out gradually. One of the works is an approach to per form charge separation in the whole film by extremely increasing the number of p-n junction portions by compounding the n-type electron conductive organic material and p-type hole conductive polymer in the film. Heerger and others have proposed in 1995 a photoelectric conversion element prepared by using a conjugate polymer as a p-type conductive polymer mixed with fullerene as an electronic conduction material (refer to Non-patent document 2). Although these photoelectric conversion elements are raising their characteristics gradually, they have not resulted in achieving the sate which operates stably with high conversion efficiency.
However, Gratzel has made a huge and detailed experimentation about the sensitized photocurrent of the dyes adsorbed on titanium oxide in 1991. He has succeeded in producing a photoelectric conversion element which achieved operational stability and exhibited high conversion efficiency by making the titanium oxide to be porous and fully securing the area of the charge separation (the number of molecules which contributes to charge separation) (refer to Non-patent document 3). In this photoelectric conversion element, iodine is used as a hole transporting agent, therefore, an electrolyte is required. This photoelectric conversion element has the stability of titanium oxide and also has excellent repeatability. As a result, the filed of research and development have been expanded greatly. This photoelectric conversion element is also called as a dye- sensitized solar cell, and this photoelectric conversion element is capturing big expectation and attention.
Although growing in size of a light receiving portion and production of an outdoor type module are indispensable for realizing the initial object of effectively using sunlight, the dye-sensitized solar cell will operate using an electrolyte as describe above, therefore, it is needed another mechanism which holds and prevents the flow and dissipation of the electrolyte or iodine. As representative examples of other electrochemical elements which have an electrolyte, a lead battery and a lithium battery are typical. Even these electrochemical elements prepared in a compact module cannot be recovered with 100% efficiency and recycled. When the dissipated chemical species are newly accumulated in an ambient, it is obvious that these species will induce a secondary problem.
There has been developed an all solid type dye-sensitized solar cell which avoided the problem of an electrolyte and succeeded the merit of the dye-sensitized solar cell. Although there are known the system using an amorphous organic hole transport agent (refer to Non-patent document 4) and the system using copper iodide as a hole transport agent (refer to Non-patent document 5) in this field, they have not achieved the level which operates stably with high conversion efficiency. Further, there is known an all solid type dye-sensitized solar cell which is provided with a bather layer between an electrode and a hole transport material layer to resolve the problem of the electric charge recombination between the electrode and the hole transport material layer which are the investigational work of all solid type dye-sensitized solar cell (refer to Patent document 1). However, it did not come to control the electric charge recombination between the titanium oxide and the hole transport material layer which was another route of electric charge recombination, and its efficiency was found to be low.